The present invention relates to an optical switch in an optical communications network and more particularly to a control system for monitoring and controlling components of the optical switch.
In an optical communications network, optical fibers carry data signals in the form of light waves modulated with information between various locations across the network. In a multi-fiber network, some of the many data signals on individual optical fibers may need to be selectively routed to other fibers. Selective routing may be required, for example, to balance communications traffic, or to avoid an out-of-service leg in the optical network. Such routing can be facilitated by interconnecting the individual optical fibers via a cross-connect switch. Cross-connect switches positioned at particular sites throughout a fiber optic communications network are used to dynamically route information signals from one location to another or to re-configure the network. In conventional cross-connects, optical signals must be converted to electrical form in order to route the signal between different optical fibers. An all-optical cross-connect switch moves optical signals between different optical fibers without the need for an intermediate conversion to electrical signals.
Currently, most types of all-optical switch fabrics, i.e. switches with no optical-to-electrical conversion, require the use of external light sources to monitor and/or control the switch fabric. The external monitors are critical to the operation of the switch fabric and provide feedback regarding the accuracy of the switch fabric in directing the data signals to the appropriate output fibers. For example, many all-optical switch fabric technologies, such as 3D-MEMS (micro electro mechanical machines), 2-D MEMS, liquid crystals, thermo-optics, holograms, liquid gratings and acousto-optics and bubble jets, require external lasers sources to monitor the performance of each light path through the switch. Some technologies, such as 3D-MEMS also require the external laser source to control the alignment of the internal optics in real time. Switches utilizing all-optical technology can potentially comprise up to many thousands of input and output ports. Each port interfaces with a fiber optic cable to direct a data signal carried by the fiber optic cable through or from the switch. Each input port requires a separate external laser source to monitor and control the optical components directing the data signals from the input port to a selected output port of the switch.
MEMS are micron-sized complex machines that have physical dimensions suitable for the fabrication of optical switches for use in communications networks. MEMS switching components generally employ an array of micro-machined steerable mirrors, fabricated on a silicon chip. Control signals applied to the MEMS chip fix the position of each mirror to direct each incoming light signal to a desired output port and output fiber. The mirror-based switches are classified according to the respective mirror movement. In 2-D MEMS switches, the mirrors have only two degrees of freedom of movement: a first degree of movement in up and down movement and a second degree of movement in side to side movement. In 3-D MEMS switches, the mirrors assume a wide variety of positions by swiveling in multiple angles and directions.
A significant disadvantage of the MEMS, in many architectures and other all-optical switches of the prior art concerns the direct association of an external laser source to each input port for monitoring and controlling the optical components of the switch. The conventional external laser source arrangement presents a single point of failure for the entire switch, as the reliability of the switch as a whole depends on the operation of each individual external laser source. When one laser source fails, a supervisory signal will not be transmitted through the corresponding input port, and the operation of the entire switch is unreliable. Consequently, expensive, highly reliable laser sources are a necessity to provide accurate and reliable monitoring and control of MEMS and other all-optical switches.
The present invention concerns a system and method for monitoring and controlling the components of a node in a communications network. The illustrative embodiment of the invention provides an active control system and method for controlling the position and/or properties of optical components in an optical switch of an optical communications network. The active control system utilizes a power-sharing scheme between an array of external light sources to control the alignment of the internal optical components of a switch in real time. According to the illustrative embodiment, a number of supervisory signals are directed through the switch to measure and regulate the switch components. The supervisory signals are produced by combining the light signals emitted by the array of external light sources, and subsequently splitting the combined signal equally to form the supervisory signals.
The illustrative embodiment of the present invention allows each supervisory signal connection through a switch to equally share the output power of all input sources in an efficient manner. As a result, the switch is tolerant of multiple laser source failures without affecting or disrupting operation. The present invention provides a scalable system and method that can be applied to small or very large all-optical switch fabrics.
According to one embodiment, a control system for monitoring and controlling optical components in a node of an optical network is provided. The control system comprises an array of external light sources configured to emit light signals and a power-sharing coupler connected to the array of light sources. The power-sharing coupler combines the light signals together to create a combined signal and subsequently splits the combined signal into a plurality of supervisory signals. The supervisory signals are utilized to control the optical components in the node.
According to another embodiment, a method of monitoring optical connections in an all-optical switch is provided. The method comprises the steps of providing an array of light sources emitting light signals, combining the light signals to form a combined signal, subsequently separating the combined signal into a plurality of supervisory signals and directing a first supervisory signal from an input port to an output port of the switch.
According to yet another embodiment, an optical switch is provided. The optical switch comprises an input port, an output port and an optical component for directing a data signal from the input port to the output port. The optical switch further includes an array of light sources for providing at least one supervisory laser signal to the node and a power-sharing coupler for combining and dividing the output of the array of light sources to form the at least one supervisory signal.
According to a final embodiment, a power-sharing coupler for directing supervisory signals through an optical switch in order to control optical components in the switch is provided. The power-sharing coupler comprises an intake manifold and a distribution manifold. The intake manifold combines a plurality of input light signals from a plurality of light sources into a combined signal. The distribution manifold splits the combined signal into a plurality of supervisory signals for monitoring the alignment of the optical components.